Composite material structure for railroad car chassis

ABSTRACT

A structure, made from composite materials for a vehicle chassis, being configured to receive an undercarriage at its ends and includes at least one central beam that includes a median box having a central part and two ends with a reinforced structure, and the central part includes a reinforced part increasing the strength of the beam with respect to the bending stresses imposed by the transported load. The median box is reinforced by two lateral boxes extending over the entire length of the median box), assembled to the median box, the upper faces of which, together with the upper face of the median box, form the upper face of the beam. The structure includes a floor that covers the upper faces of the median box and the lateral boxes. The elements making up the structure have shapes that are simple, easy to make from composite materials and easy to assemble.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/EP2014/066236, having an international Filing Date of 29 Jul. 2014,which designates the United States of America, and which InternationalApplication was published under PCT Article 21(2) as WO Publication No.2015/014819 A1, and which claims priority from and the benefit of FrenchApplication No. 13576.88, filed 2 Aug. 2013, the disclosures of whichare incorporated herein by reference in their entireties.

BACKGROUND

1. Field

The disclosed embodiment relates to the general field of rolling stockstructures. The disclosed embodiment relates more particularly to acomposite beam design intended, by using composite materials, to reducethe weight of the structure of a rail transport vehicle (railroad car),notably for transportation of freight by rail.

2. Brief Description of Related Developments

As is the case in all transport fields, the railroad car constructionsector seeks to reduce the mass of the structures forming the vehicle inorder to increase the payload and/or to reduce transportation coststhrough controlling both the production costs of the vehicles and theirenergy consumption.

At present railroad cars are formed exclusively of metal structures,generally of steel and sometimes aluminum.

Where transport is concerned, however, it is only natural. to envisagelighter aspects, in particular using composite materials. However, it isalso known that it is not possible, through simple substitution ofmaterials, to replace a metal structure with a composite materialstructure of identical shape. It is generally necessary to redesign thestructures completely to exploit all the technical characteristics andproperties specific to composite materials.

The necessity to redesign these structures in the context of the use ofcomposite materials notably concerns the particular features describedhereinafter.

A first particular feature to be considered is the anisotropic characterof composite materials, as a result of which their properties, inparticular their mechanical properties, are not identical in alldirections, because of the presence of the reinforcing fibers of whichthe material is composed. Such a particular feature imposes thedefinition of a material architecture suited to each application.

Another particular feature to be considered is the variety ofmanufacturing processes employed (molding, vacuum infusion, RTM (ResinTransfer Molding), draping, etc.) and that the assembly techniques usedto assemble composite material. elements are generally specific to thosematerials. In contrast to what is the case with metals, it is in facthardly feasible to weld heat-setting composite materials, for example,but it is entirely appropriate to assemble such materials by gluing,which is exactly the opposite of what it is possible to achieve withmetals.

A further particular feature resides in the specifics of the variousvariants of composite materials that are available, in particular wherethe nature of the fibers used is concerned, whether mineral fibers(glass fibers, carbon fibers, etc.) or organic fibers, the nature ofwhich confers on the corresponding composites different properties,behaviors and costs. Thus composite materials based on glass fibers arethe least costly whereas carbon fiber composites appear the most costly.

Because of these particular features, the use of composite materialstructures to produce rolling stock capable of transporting heavy loadshas at present not been developed much or at all, in particular wherethe manufacture of railroad cars, notably freight cars, is concerned.

It is pointed out here that the composite materials concerned areso-called “structural” composite materials which are based on long andcontinuous fibers that represent approximately 50% of the material, theother approximately 50% consisting of a matrix, generally a heat-settingresin, of epoxy (EP), diallyiphtalate (DAP), polyester OT vinylestertype, for example, and, more rarely, a thermoplastic resin, ofpolyamide, PEEK or PEI type, for example.

SUMMARY

One object of the disclosed embodiment is to propose a particularcomposite material structure that can be used to manufacture vehiclessuch as those referred to above. In particular, one object of thedisclosed embodiment is to define a railroad car platform structure theshape characteristics of which are optimized to enable its manufacturefrom composite materials.

Here the final objective is to reduce significantly the mass of thestructure of a railroad car, at the same time as optimizing themanufacturing costs for performance in terms of robustness equal to orbetter than the performance of current structures.

To this end, the disclosed embodiment consists in a composite materialstructure, for chassis of vehicles for transporting freight orpassengers, said structure. being configured to accept running gear or abogie at each of its ends, said structure including at least one centralbeam forming a platform on which the load of the vehicle rests. Inaccordance with the disclosed embodiment, said beam includes:

a middle box having a central portion and two ends, said ends havingreinforcements to withstand the stresses transmitted to the chassis bythe articulation elements of the running gear and by the shock absorberelements disposed at the ends of the vehicle, the central portion of themiddle box being configured so as to have a reinforced portionincreasing the resistance of the beam to bending forces imposed by thetransported load;

two lateral boxes extending over all the length of the middle box,assembled to said middle box, the upper faces of Which form with theupper face of the middle box the upper face of the beam, said lateralboxes being configured so as to reinforce the resistance of the beam tolongitudinal and transverse bending forces imposed on it;

a covering floor forming a skin, configured so as to cover the upperfaces of the middle box and the lateral boxes.

In accordance with the disclosed embodiment, the various elementsconstituting the beam are made of composite materials reinforced withglass fibers or carbon fibers or a mixture of glass fibers and carbonfibers.

In accordance with various features that may be considered separately orin combination, the structure in accordance with the disclosedembodiment has various complementary features. Accordingly:

In accordance with one particular feature, the middle box consists of anupper half-box extending over all the length of the beam and a lowerhalf-box disposed in the central portion, the two half-boxes eachincluding a bottom and two lateral walls. The upper half-box and thelower half-box are arranged relative to each other so that the bottom ofthe upper half-box forms the upper face of the middle box and the bottomof the lower half-box forms the lower face of said box. The bottom ofthe lower half-box moreover extends externally thereof toward the endsof the beam.

In accordance with another particular feature, a composite materialintermediate partition is placed between the upper half-box and thelower half-box so as to reinforce the stiffness of the middle box andthe resistance to buckling of the lateral walls of the upper half-boxand of the lateral walls of the lower half-box.

In accordance with another particular feature, the covering floorconsists of a principal element (61) in the form of a monolithiccomposite material plate reinforced with glass fibers including in itsmiddle portion a composite material reinforcing element (52) sized so asto cover the upper face of the middle box (314).

In accordance with another particular feature, the bottom of the upperhalf-box, the bottom of the lower half-box and a middle reinforcingelement of the principal element of the skin disposed on the upper faceof the structure are made of monolithic composite material reinforcedprimarily with unidirectional fibers, said fibers preferably beingcarbon fibers.

In accordance with another particular feature, the structure inaccordance with the disclosed embodiment further includes compositematerial lateral reinforcements disposed on either side of the beam andadapted to absorb forces applied to the lateral portions of thestructure by the transported load. Each reinforcement is fastened to alateral box by one of its ends and to the middle box by its other end.

In accordance with another particular feature, the elements forming thebeam consist of composite material plane faces.

In accordance with another particular feature, the upper half-boxincludes a bottom consisting of a monolithic composite material plateand lateral walls with a sandwich structure consisting of two compositematerial thin skins reinforced with glass fibers and a core consistingof an element formed of polymer material foam or a honeycomb structurematerial or a balsa type wood.

In accordance with another particular feature, the lower half-boxincludes a bottom consisting of a monolithic composite material plateand lateral walls with a sandwich structure consisting of two compositematerial thin skins reinforced with glass fibers and a core consistingof an element made of polymer material foam or a honeycomb structurematerial or a balsa type wood.

In accordance with another particular feature, the lateral reinforcingelements have a sandwich structure consisting of two composite materialthin skins reinforced with glass fibers and a core consisting of anelement made of polymer material foam or a honeycomb structure materialor a balsa type wood.

In accordance with another particular feature, the various elements ofthe structure in accordance with the disclosed embodiment include rimsadapted to enable the assembly of said elements by gluing and/or boltingand/or riveting, two elements assembled to each other having rimsadapted to be placed face-to-face at the time of assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the disclosed embodiment will be betterappreciated thanks to the following description with reference to theappended figures, which show:

FIGS. 1 and 2 are diagrammatical illustrations showing the theoreticalstructure of the chassis in accordance with the disclosed embodiment inlateral view and in frontal section at the level of the middle portionof the chassis;

FIG. 3 is a diagrammatic lateral view, in section, of one chassisembodiment in accordance with the disclosed embodiment;

FIG. 4 is a diagrammatic view in cross section of the chassis from FIG.3, in a plane passing through the central area of the structure;

FIG. 5 is a diagrammatic view in cross section of the chassis from FIG.3, in a plane passing through one end of the structure;

FIG. 6 is a diagrammatic view in cross section of the platformsurmounting the structure of the chassis in accordance with thedisclosed embodiment, in the FIG. 3 aspect;

FIG. 7 is a diagrammatic view in cross section of the upper half-boxconstituting the beam of the chassis in accordance with the disclosedembodiment, in the same aspect;

FIG. 8 is a diagrammatic view in cross section of the lower half-boxconstituting the beam of the chassis in accordance with the disclosedembodiment, in the same aspect;

FIG. 9 is a diagrammatic view in cross section of a lateral boxconstituting the beam of the chassis in accordance with the disclosedembodiment, in the same aspect;

FIG. 10 is a diagrammatic view in cross section of a lateralreinforcement panel that can be integrated into the beam of thestructure of the chassis in accordance with the disclosed embodiment;

FIG. 11 is a diagrammatic illustration of various steps of assemblingthe structure in accordance with the disclosed embodiment.

DETAILED DESCRIPTION

The purpose of the diagrammatic FIGS. 1 and 2 is to show the theoreticalstructure of the chassis in accordance with the disclosed. embodiment.In accordance with this principle, the chassis in accordance with thedisclosed embodiment primarily includes an upper platform 11 intended tosupport the transported load 13, having reinforcements 111 and 112 atthe ends, and a lower box 12, or reinforcement, situated under thecentral portion of the platform 11 and intended to confer an increasedstiffness in the central portion of the assembly, in particular in termsof longitudinal and transverse bending.

For their part, the reinforcements at the ends have the principalfunction of absorbing forces imposed on the structure at the level ofthe axes 113 and 114 about which the chassis is articulated to therunning gear (bogies) of the vehicle as well as absorbing forces towhich the vehicle, the railroad car, is subjected at the level of thecouplings, the shock absorbers or buffers at the ends, etc.

In accordance with the disclosed embodiment, the various structuralelements of the chassis are made of composite materials. The structureof each of the elements is moreover defined so that the portions havingto be subjected to in-plane stresses are constituted by single compositematerial webs of monolithic structure, preferably including areinforcement by fibers oriented longitudinally, whereas the portions ofan element having to be subjected to out-of-plane stresses, for exampletorsion stresses, have a sandwich structure formed of two compositematerial skins separated by an interleaved element, a core, consistingof a filler material, preferably as light as possible, for example a PS,PVC, PU, PET type polymer material foam, or a honeycomb structurematerial or a wood of low density, for example of balsa type.

Depending on the stresses that the structural element concerned has towithstand, the fibers constituting the reinforcement of the compositematerial used are either glass fibers or carbon fibers, eitherunidirectional (UD) fibers or woven fibers (mat) that are stacked asrequired. The structure of each panel, i.e. the choice of the plies,their orientation in the material, their stacking is carried out usingsimulation tools well known to the person skilled in the art, knowingthat what is still looked for is optimization of the part that is beingdesigned in terms of mass and production cost.

The following description features one aspect of a railroad car chassisconstructed on this typical structure. The purpose of this example is toshow clearly the particular technical features of the disclosedembodiment. The scope of the disclosed embodiment is not limited to theframework of this example alone, of course.

As FIGS. 3 to 5 show, in this aspect the railroad car chassis inaccordance with the disclosed embodiment consist primarily of a beam 31that combines the functions of the upper platform 11 and the bottom box12 of the theoretical structure described above, the beam 31 beingcovered by a coating 32.

The coating 32, or skin, is a relatively thin plane composite materialelement the dimensions of which are defined so that it covers all of thesurface of the structure (of the chassis). In a preferred aspect, theskin 32 consists of a composite material plane first element 321reinforced with glass fibers having a middle portion reinforced on itslower face, by a composite material plane, second element 322 alsoreinforced with glass fibers. In particular aspects, however, the secondelement 322 may equally well be made from a composite materialreinforced with carbon fibers, where, appropriate UD fibers, so asnotably to have greater mechanical strength (in particular intraction/compression and in bending) and a higher strength-to-weightratio.

For its part, the beam 31 forming the platform has a central. portion311 and two areas 312 and 313 at the ends to which the running gear ofthe vehicle is articulated, in other words the bogies of the railroadcar in the present example. From a structural point of view, the centralportion 311 and the two ends 312 and 313 of the beam 31 consist of oneand the same composite material element integrating reinforcing elements35, 36 at its ends, as shown by FIGS. 3 and 5. These reinforcing takingthe form of composite material webs or beams, are notably intended toreinforce the area of connection and articulation to the bogies and thetransmission of forces applied to the buffers.

In this aspect, the beam 31 in accordance with the disclosed embodimentconsists of a middle box 314 and two lateral boxes 315, 316 situated atrespective, opposite longitudinal ends of the middle box 314 andassembled to the middle box 314.

In accordance with the variant aspect considered here, the middle box314 may be made in one piece. Nevertheless, for reasons of ease ofmanufacture in particular, it is preferably produced in two parts, anupper half-box 317 extending over all the length of the railroad car anda lower half-box 318 that reinforces the upper half-box 317 in thecentral area 311 of the beam 31. The upper half-box forms both thecentral portion 311 and the reinforced ends 312 and 313 of the beam 31.

The lower half-box 318, situated only in the central portion of therailroad car, has a lower wall 319 the function of which is to reinforcethe bending inertia of the assembly.

To this end, as FIG. 3 shows, this wall 319 is extended beyond thelimits of the lower half-box 313 as far as the areas 312 and 313 at theends of the upper half-box 317 so as to close said upper half-box andthereby participate in the absorption of forces notably imposed by thepivots of the bogies.

The height of each half-box, in particular that of the lower half-box313, is defined as a function of the manufacturing choices adopted torespond to the mechanical stresses that the structure must withstand, inparticular the weight of the load.

For their part, the lateral boxes 315 and 316 are elements continuousover all the length of the car. Situated on respective opposite sides ofthe upper half-box 317, they constitute with it the upper face of thebeam 31 on which the skin 32 rests. They further contribute to theresistance to longitudinal and transverse bending of the chassis formedin this way and participate in the absorption of forces in line with thebuffers.

In one particular aspect, shown by FIG. 4, the central portion of thebeam 31 is moreover reinforced laterally by composite material lateralelements 33 and 34 disposed obliquely which, in accordance with thevariant aspect considered here, clothe this central portion continuouslyover all its length and form two lateral reinforcing walls, or,alternatively, constitute localized reinforcements, forming obliquereinforcing bars spaced from one another along the central portion ofthe beam 31. These, reinforcing elements 33 and 34 serve to absorbtransverse, bending forces and thus limit any twisting of the structure.

It should be noted that, depending on the respective, heights of theupper and lower half-boxes, it is possible in one particular aspect toadd an intermediate plate to stabilize the middle box 314 produced fromthese two half-boxes 317 and 318, the function of this intermediateplate or partition being to prevent buckling of the lateral partitionsof the upper and lower half-boxes.

FIGS. 6 to 10 show the morphological and structural characteristics ofthe various elements described above.

As shown by FIG. 6, the panel constituting the skin 32 disposed on theupper face, of the structure consists of a plane, principal element 61covering by virtue of its dimensions the whole of the surface formed bythe upper faces of the middle box 314 and the lateral boxes 315 and 316and a middle reinforcing element 62, also plane, disposed facing theupper face of the middle box 314.

In accordance with the aspect envisaged here, the principal element 61may be made of a composite material reinforced with glass fibers, forexample, like the reinforcing element 62. However, in particularaspects, the second element 62 may equally well be made from a compositematerial reinforced with carbon fibers, where appropriate UD fibers, soas to have greater mechanical strength (in particular intraction/compression and in bending) and a higher strength-to-weightratio.

The illustrations in FIGS. 7 and 8 show in detail the morphology and thestructure of the upper half-box 317 and the lower half-box 318 thatconstitute the middle box 314.

The upper half-box 317 is primarily formed of a bottom 71 consisting ofa composite material monolithic wall and two lateral walls 72 and 73,these walls extending over all the length of the middle box. Themonolithic bottom 71 may in accordance with the aspects envisaged hereconsist of two composite material skins (76, 77) reinforced with glassfibers, the reinforcement primarily consisting of UD layers of glassfibers, or alternatively, notably for reasons of mechanical strength andhigher strength-to-weight ratio, composite material reinforced withcarbon fibers. For their part, the two lateral walls 72 and 73 have asandwich structure formed of the two composite material skins 76,separated by an interleaved element 78, a core, consisting of a fillermaterial, a PS, PVC, PU, PET type polymer material foam, for example, ora honeycomb structure material or a wood of balsa type, for example.Their sandwich structure enables the lateral walls to have betterstability in terms of buckling.

As may be noted on considering FIGS. 3, 4 and 5, the general shape ofthe upper half-box 317 is that of a parallelepiped with an open faceopposite the face forming the bottom 71.

In accordance with a preferred aspect, the lateral walls 72 and 73 fortheir part each have a rim 74 or 75 extending laterally toward theexterior of the half-box over all the length of the latter, this rimbeing used to carry out the assembly of the complete chassis.

Like the upper half-box, the lower half-box 318 consists primarily of abottom 81 and two lateral walls 82 and 83 that border the centralportion of the middle box 314. Like the walls 72 and 73 of the upperhalf-box, the two lateral walls 82 and 83 here have a sandwichstructure.

The bottom 81, which, as stated above, extends over all the length ofthe structure and which has the function of reinforcing the bendinginertia of the whole of the structure (of the chassis) also has amonolithic structure consisting, in accordance with the aspectsenvisaged here, of the two composite material skins reinforced withglass fibers, the reinforcement consisting primarily of UD layers ofglass fibers, or alternatively, notably for reasons of mechanicalstrength and higher strength-to-weight composite material reinforcedwith carbon fibers.

From a morphological point of view, the lower half-box 318 has a prismshape with trapezoidal bases which represent the lateral walls 82 and 83of the half-box. For their part the front and rear faces of the half-boxconsist of the bottom 81 that is extended obliquely toward the front andtoward the rear, beyond the lower half-box 318, so that its rims 74 and75 come progressively into contact with the upper half-box 317, as shownby FIG. 3, for example.

In one preferred aspect, illustrated by FIGS. 7 and 8, the lateral walls72 and 73 each have for their part a rim or 85 extending laterallytoward the exterior of the half-box concerned over all the length of thelatter, this rim being used to carry out the assembly of the completechassis. Similarly, the lateral walls 82 and 83 each have a rim 84 or 85extending laterally toward the exterior of the half-box over all thelength of the latter.

For its part, the bottom 81 has on its portion extending out of thelower half-box flat rims 86 and 87 used to carry out the assembly of thecomplete chassis. The rims 86 and 87 are configured and arranged so thatthey are positioned, at the level of the ends of the structure, facingthe rims 74 and 75 of the lateral walls of the upper half-box 317.Similarly, for their part the rims 84 and 85 are configured and arrangedso that they are positioned, at the level of the central portion of thestructure, facing the rims 74 and 75 of the lateral walls of the upperhalf-box 317. The presence of such rims advantageously facilitates theassembly of the lower half-box 318 and the upper half-box 317 to form asingle middle box 314. This assembly may be effected by gluing the rims,for example, or by riveting or by bolting, or by gluing-plus-rivetingthese same rims.

From a morphological point of view, the lateral boxes 315 and 316 have,identical shapes. As FIG. 9 shows, each box includes a vertical internallateral wall 91 intended to come into contact with one of the lateralwalls of the upper half-box 317 and an oblique external lateral wall 92forming an external upper edge of the chassis. The oblique orientationof the external lateral wall advantageously makes it possible to producea bearing engagement without adjustment to assemble the lateral elements33 and 34. The lateral walls of a lateral box are joined to one anotherby a flat bottom 93 parallel to the plane of the bottom 71 of the upperhalf-box.

From a structural point of view, the lateral box walls consist, like thelateral walls of the upper half-box 317 and the lower half-box 318, oftwo composite material skins reinforced with glass fibers separated by acore made from a filler material, polymer material foam or honeycombstructure material, or wood, for example of balsa type.

In accordance with one particular aspect, filler material may moreoverbe integrated into the boxes 315 and 316, a material consisting ofpolymer material foam or a honeycomb structure material or wood of balsatype for example. This material makes it possible to loin the internalskins 91-92-93 of the lateral boxes 315-316 to one another and to theskin placed on the upper face of the platform 32.

Also from a structural point of view, the composite material lateralreinforcing elements 33 and 34 intended to reinforce the resistance totwisting and to bending (longitudinally and transversely) of thestructure of the chassis in accordance with the disclosed embodimentalso consist, like the lateral walls of the upper half-box 317 and thelower half-box 318, of two composite material skins reinforced withglass fibers separated by a core made of polymer material foam or ahoneycomb structure material or wood of balsa type for example. In apreferred aspect shown in FIG. 10 the body 101 of the reinforcement isextended by rims 102 and 103 arranged relative to the body 101 so as tofacilitate the assembly of the reinforcing element concerned with theexternal lateral wail of the corresponding lateral box 315 or 316 andwith the lateral wall of the lower half-box 318. This assembly may beeffected by gluing the rims, for example, or by riveting or by bolting,or by gluing-plus-riveting these same rims.

As can be seen in FIGS. 6 to 10, the chassis structure in accordancewith the disclosed embodiment, as described in the foregoing text, hasthe important advantage of consisting of elements having both a simplemorphology that is easy to assemble (faces and bearing engagements onplane faces) and an internal structure that is easy to manufacture.These features advantageously make it possible to facilitate theassembly of such a structure, despite the sometimes large dimensions ofthe latter.

The composite material elements forming the structure in accordance withthe disclosed embodiment being elements of simple shape having planefaces, the structure in accordance with the disclosed embodiment mayadvantageously be constructed in a simple manner and at relatively lowcost, the various composite material elements constituting the structurecan be manufactured using simple processes, primarily by drapingpre-impregnated fibers and/or dry fibers, combined with vacuumpolymerization or RTM, or by infusion given the large size of themanufactured elements, such as those employed in the production windturbine blades, for example.

Moreover, given the composite structure concept of the disclosedembodiment, the assembly of the various composite elements constitutingthe chassis in accordance with the disclosed embodiment isadvantageously simple to carry out in that all the connections occuralong plane and linear bearing surfaces provided for this purpose,assembly being achievable using relatively simple tools, by gluing, orby riveting or by bolting, or by gluing-plus-riveting the variouselements to one another, for example.

FIG. 11 shows diagrammatically the method of assembling a chassisstructure in accordance with the disclosed embodiment from constituentelements described above, which method includes:

-   -   a first step (step 1) that consists in assembling the upper        half-box 317 and the lower half-box 318 to form the middle box        314;    -   a second step (step 2) which consists in assembling the lateral        boxes 315 and 316 to the middle box 314 to constitute the beam        31 forming the platform of the structure, assembly taking place        at the level of the upper half-box 317; where appropriate having        incorporated into the boxes 315-316 a filler material consisting        of a polymer material foam or a honeycomb structure material or        wood o balsa type for example;    -   a third step (step 3) consisting in fixing the skin 32 to the        upper face of the beam 31 so as to cover the upper faces of the        upper half-box 317 and the lateral boxes 315 and 316;    -   a fourth step (step 4) consisting, where appropriate, in fixing        the lateral reinforcing elements 33 and 34 to the beam 31.

It should be noted that, when the chassis produced actually includeslateral reinforcing elements, steps 3 and 4 may be interchanged.Moreover, in accordance with the aspects envisaged here, steps 1 to 4may be carried out in a different order, for example 2, 3, 1, 4 or 3, 2,1, 4.

It should also be noted that, during the second step, the upper half-box317 and the lower half-box 318 may be assembled with an intermediateplate interleaved between the two half-boxes, where the rims 74-75 and84-85 loin, as described above, the function of this plate being toreinforce the stiffness of the assembled beam.

In accordance with the disclosed embodiment, the composite beam 31produced in this way integrates at its ends, at the level of thereinforcements, metal elements the function of which is notably toprovide the interface with the bogies and with the buffers at the ends.The metal elements are fixed to the composite material structure inaccordance with the disclosed embodiment by appropriate fixing means(bolts and/or rivets), for example using an appropriate technique ofassembly between metal parts and composite material parts, like thatdescribed in the applicant's patent FR 2 948 154.

Thereafter the complete production of a chassis in accordance with thedisclosed embodiment also includes an operation of placing and fixinginterface elements on and to the beam 31, at the level of the ends ofthe boxes 315, 316 and 317, which operation may, depending on theproduction method adopted, be carried out on the boxes before assemblyor during assembly, for example after step 2.

As is clear from the foregoing description, this disclosed embodimentmay be. used on all types of rail vehicle intended for thetransportation of freight (railroad cars) or passengers. It may equallywell be used to produce road freight vehicle chassis, in particularheavy goods vehicle trailers.

What is claimed is:
 1. A composite material structure, for chassis ofvehicles for transporting freight, or passengers, said structure beingconfigured to accept running gear at each of its ends, the structureincludes at least one central beam forming a platform on which the loadof the vehicle rests, said beam including: a middle box having a centralportion and two ends, said ends having reinforcements for withstandingthe stresses transmitted to the chassis by the articulation elements ofthe running gear and by the shock absorber elements disposed at the endsof the vehicle, the central portion of the middle box being configuredso as to have a reinforced portion increasing the resistance of the beamto bending forces imposed by the transported load; two lateral boxesextending over all the length of the middle box, assembled to saidmiddle box, the upper faces of which form with the upper face of themiddle box the upper face of the beam, said lateral boxes beingconfigured so as to reinforce the resistance of the beam to longitudinaland transverse bending forces imposed on it; a covering floor forming askin, configured so as to cover the upper faces of the middle box andthe lateral boxes; The various elements constituting the beam being madeof composite materials reinforced with glass fibers or carbon fibers ora mixture of glass fibers and carbon fibers.
 2. The structure as claimedin claim 1, wherein the middle box consists of an upper half-boxextending over all the length of the beam and a lower half-box disposedin the central portion, the two half-boxes each including a bottom andtwo lateral walls, the upper half-box and the lower half-box beingarranged relative to each other so that the bottom of the upper half-boxforms the upper face of the middle box and the bottom of the lowerhalf-box forms the lower face of said box, the bottom of the lowerhalf-box extending externally thereof toward the ends of the beam. 3.The structure as claimed in claim 2, wherein a composite materialintermediate partition is placed between the upper half-box and thelower half-box so as to reinforce the stiffness of the middle box andthe resistance to buckling of the lateral walls of the upper half-boxand of the lateral walls of the lower half-box.
 4. The structure asclaimed in claim 1, wherein the covering floor consists of a principalelement in the form of a monolithic composite material plate reinforcedwith glass fibers including in its middle portion a composite materialreinforcing element sized so as to cover the upper face of the middlebox.
 5. The structure as claimed in claim 1, wherein the bottom of theupper half-box, the bottom of the lower half-box and a middlereinforcing element of the principal element of the skin disposed on theupper face of the structure are made of monolithic composite materialreinforced primarily with unidirectional fibers, said fibers preferablybeing carbon fibers.
 6. The structure as claimed in claim 1, furtherincludes composite material lateral reinforcements disposed on eitherside of the beam and adapted to absorb forces applied to the lateralportions of the structure by the transported load, each reinforcementbeing fastened to a lateral box by one of its ends and to the middle boxby its other end.
 7. The structure as claimed in claim 1, wherein theelements forming the beam consist of composite material plane faces. 8.The structure as claimed in claim 2, wherein the upper half-box includesa plane bottom consisting of a monolithic composite material plate andtwo lateral walls with a sandwich structure consisting of two compositematerial thin skins reinforced with glass fibers and a core consistingof an element formed of polymer material foam or a honeycomb structurematerial or a balsa type wood.
 9. The structure as claimed in claim 2,wherein the lower half-box includes a bottom consisting of a monolithiccomposite material plate and lateral walls with a sandwich structureconsisting of two composite material thin skins reinforced with glass.fibers and a core consisting of an element made of polymer material foamor a honeycomb structure material or a balsa type wood.
 10. Thestructure as claimed in claim 6, wherein the lateral reinforcingelements have a sandwich structure consisting of two composite materialthin skins reinforced with glass fibers and a core consisting of anelement made of polymer material foam or a honeycomb structure materialor a balsa type wood.
 11. The structure as claimed in claim 1, whereinthe various elements of said structure include rims adapted to enablethe assembly of said elements by gluing and/or bolting and/or riveting,two elements assembled to each other having rims adapted to be placedface-to-face at the time of assembly.